It has since gone into newslore and remains a popular and effective PR 'news hook' to this day.

Last week's Daily Mail story was trying to sell us windows:

"A new study suggests say there may be a simple way of combating 'Blue Monday' - sit by a window… Melanie McDonald, of Anglian Home Improvements, which commissioned the study, said: "The survey shows a clear link between natural daylight, mood and motivation."

This week's 'Blue Monday' story in the Daily Mail was based on exactly the same research from Anglian Home Improvements.

Now, if anything tells us how arbitrary this day really is it's the fact the same newspaper can't seem to decide from one week to the next which day it should fall on and doesn't remember running exactly the same story the previous week.